In a gate manufacturing process of a flash memory (such as 3D-NAND) having a three-dimensional structure, as disclosed in PTL 1, along with the increase in device capacity, the total number of pair layers of a polysilicon film and a silicon oxide film is increasing to 48 layers, 72 layers, 96 layers, and 120 layers, and a high aspect ratio plasma etching processing is progressing.
Conventionally, when these laminated films are etched, a laminated film of a patterned photoresist film (PR), an antireflection film (bottom anti-reflection coat (BARC)), and an amorphous carbon film (amorphous carbon layer (ACL), hereinafter called an ACL film) has been used as an etching mask. However, with the increase in the aspect ratio, the thickness shortage of a mask of the amorphous carbon film becomes obvious.
Therefore, a B-doped ACL film is applied in which an ACL film is doped with (contains) boron element (B), and boron improved in plasma resistance is contained. When a conventional ACL film is etched, a resist pattern is transferred to an ACL film by adding COS or nitrogen by using oxygen as a main component or by using plasma diluted with argon or helium. However, it has been difficult to etch a 10 to 40% boron-containing B-doped ACL film in this gas system.
To solve this problem, PTL 2 discloses a method for performing etching by increasing volatility of a reaction product of boron by setting the temperature of a wafer stage to 100° C. or higher, and PTL 3 discloses a method for etching at room temperature of 10 to 30° C. by converting to boron fluoride by using a mixed gas of CH4, Cl2, SF6, and O2, by increasing the volatility of the reaction product, and by controlling process perpendicularity by Cl2 and CH4.